1. Field of the Invention
The present invention concerns guided missiles or projectiles and more specifically a gas propellor using a solid propellant and comprising a plurality of nozzles, the relative flow rates of which can be caused to vary in order to alter the flight path of the missile or projectile.
The maneuvering capacity of offensive targets is constantly being improved which means that any interception error (or passage distance) of the projectiles or missiles is consequently increased. During the launch or firing of a missile or projectile, it is necessary to consider the cruising phase during which it is desired to maintain the displacement speed of the projectile, and the terminal phase during which the measured trajectory error must be cancelled out or at least reduced to a value compatible with the efficiency radius of the military charge, which radius can perhaps be zero in the case of a hollow charge.
2. Prior Art
In a guided missile or projectile, it is often advantageous, especially for reasons of weight and costs of the weapons system, to combine into a single propellor device means for allowing the maintenance of the displacement speed and for allowing the projectile to deviate in its trajectory. If the choice of the type of propellant, either solid or liquid, is now considered, it will be observed that this choice is imposed by operating restrictions, which usually lead to selecting solid propellants due to their extended storage capacity. On the other hand, an inherent difficulty in using solid propellants results from the fact that once the combustion has been completely initiated, the combustion pressure must be maintained within relatively narrow limits. A drop in combustion pressure, resulting from too high a gas flow-rate, leads to firing-out the propellor. On the contrary, an increase of the combustion pressure resulting from a decrease of the gas flow-rates provokes accidental explosion of the propellor.
More generally, it is known to deviate the flight trajectory of a missile of projectile by controlling the relative flow-rates of the gas jets supplied by a nozzle assembly suitably disposed at the periphery of the projectile body. It is also known to direct the nozzles towards the rear of the projectile in order to create jointly a longitudinal thrust force and a lateral thrust force.
Solid propellant propellors intended to supply two components of mutually orthogonal force have already been proposed. One component is a longitudinal thrust force of fixed magnitude, and the second component is a magnitude and direction controlled lateral thrust. Solid propellant guiding propellors can be divided into two distinct classes according to the method of operating the means for controlling the relative flow-rates of the gas jets of the nozzles. In a first class, as disclosed in U.S. Pat. No. 4,017,040, each pair of diametrically opposed nozzles is provided with a valve having three stable positions; first and second positions for which the gas flow is directed into one or other of nozzles, and a third position for which the gas flow is delivered at equal rates into the two nozzles. In the second class, illustrated by the device disclosed in French patent application filed under No. 82 21227 on Dec. 17, 1982, each pair of nozzles is provided with a valve having two stable positions and operating according to an "all or nothing" alternate cycle. By varying the cyclic rate of opening the valve, the gas flow can be controllably distributed between the two diametrically opposed nozzles.
The gas propellors of the prior art do not fully overcome the problem raised by the conception of a gas propellor for a guided missile or projectile. The aim of the present invention is to obtain a gas propellor, the operating conditions of which differ according to whether the missile or projectile is in the cruising phase of its trajectory or in the terminal guiding phase to the target.